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Marantz discrete op amp (line stage or headphone amp)

Posted 10th November 2013 at 12:00 PM by rjm
Updated 10th November 2013 at 02:11 PM by rjm

Last one for today.

I was having problems getting this to work, the key seems to be adjusting R6 to null the voltage offset. Works fine now, but this is just a rough reverse engineer of the diagram, the parts values and the type of transistors are essentially placeholders.

The input jFET is shown as a dual package. The output bias current is most likely much lower than the 100 mA I configured, so the class A output power is proportionately smaller. For the rest of the currents and the types of transistors used, your guess is as good as mine.

edit: R7 should most likely be closer to 47 ohms, while another 5p capacitor should go in parallel with the feedback resistor, R17.
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rjm
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Posted in The Lab
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Old

The Pentamond

Posted 10th November 2013 at 06:17 AM by rjm

A rainy and cold afternoon here in Kyoto. The mind turns to audio circuits... headphone amplifiers... diamond buffers...

This is an answer to the question of how you scale up the basic diamond buffer circuit to higher output currents without making any modifications to the driving transistor pair.

You just add more outputs in parallel.

It seems to work pretty well under simulation.
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Posted in The Lab
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Old

Another diamond buffer variant

Posted 10th November 2013 at 12:42 AM by rjm

Browsing through an old issue of MJ (No. 1076), I found some sketches of the Marantz SA 11S3 SACD player analog circuitry which seemed interesting.

The are two discrete op amp "modules", one is used for the I/V converter and low pass filter, the other design is applied to both the line output and headphone outputs.

The parts and values are not given, so the circuit below is just a working mock up in LTSpice based on the published diagrams.

The output stage from the headphone / line driver op amp is attached below. There's a JFET input and BJT gain stage as well, and the whole thing is wrapped up in a feedback loop. The buffer itself, being unity gain, works just fine as a standalone circuit element.
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Posted in The Lab
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